NS systems are devices that generate electrical pulses and deliver the pulses to nervous tissue to treat a variety of disorders. For example, SCS has been used to treat chronic and intractable pain. Another example is deep brain stimulation, which has been used to treat movement disorders such as Parkinson's disease and affective disorders such as depression. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of electrical pulses depolarize neurons and generate propagating action potentials into certain regions or areas of nerve tissue. The propagating action potentials effectively mask certain types of pain transmitted from regions, increase the production of neurotransmitters, or the like. For example, applying electrical energy to the spinal cord associated with regions of the body afflicted with chronic pain can induce “paresthesia” (a subjective sensation of numbness or tingling) in the afflicted bodily regions. Inducing this artificial sensation replaces the feeling of pain in the body areas effectively masking the transmission of non-acute pain sensations to the brain.
Aβ sensory fibers mediate sensations of touch, vibration, and pressure from the skin. Aβ sensory fibers have been shown to be recruited at therapeutic stimulation levels and the amplitude of the Aβ potential correlates with the degree of coverage of the painful area or region. Further, the amplitude of the Aβ potential has been shown to increase with increasing stimulation current from the SCS. At high currents, additional late responses have been observed.
A concern of SCS system designs are neural damage caused by the generated electrical pulses emitted from lead electrodes of the SCS system. Conventional SCS systems are configured such that the lead electrodes are charge-balanced after the electrical pulses are emitted. However, an electrode may be polarized during deliver of the pulse that irreversible tissue damage or electrode damage can occur. Therefore, a need remains to determine a limit for the current and charge densities of the generated electrical pulses that allow charge injection be compensated by reversible processes.